Counter-Rotating Hands Pelvis Collapse

Complete Practice

Stand. Initiate a small horizontal circle with the right hand at hip height, one cycle per second. Now reverse the direction of the left hand simultaneously. The two hands are counter-rotating oscillators sharing a pelvis. Drop the right hand's radius progressively while holding its period; observe whether the pelvis tracks the larger circle (the left), the smaller one (the right), or attempts both and jams. The perception task: find the radius ratio at which the pelvis lane-collapses — picks one as the dominant signal — and watch the side-step it takes to commit.